story the other
way and regard the salmon as a member of a freshwater race, that has
taken to the sea for feeding purposes. In regard to trout, we know that
the ranks of those in rivers and lakes are continually being reinforced
by migrants from the sea, and that some trout go down to the sea while
others remain in the freshwater. We know also in regard to a related
fish, the char, that while the great majority of kinds are now permanent
residents in cold and deep, isolated northern lakes, there are Arctic
forms which live in the sea but enter the rivers to spawn. These facts
favour the view that the salmon was originally a marine fish. But there
are arguments on both sides, and, for our present purpose, the important
fact is that the salmon is conquering _two_ haunts. Its evolution is
going on.

The Romance of the Eel

Early in summer, at dates varying with the distance of the rivers from
the open Atlantic, crowds of young eels or elvers come up-stream.
Sometimes the procession or eel-fare includes thousands of individuals,
each about the length of our first finger, and as thick as a stout
knitting needle. They obey an inborn impulse to swim against the stream,
seeking automatically to have both sides of their body equally
stimulated by the current. So they go straight ahead. The obligation
works only during the day, for when the sun goes down behind the hills
the elvers snuggle under stones or beneath the bank and rest till dawn.
In the course of time they reach the quiet upper reaches of the river or
go up rivulets and drainpipes to the isolated ponds. Their impulse to go
on must be very imperious, for they may wriggle up the wet moss by the
side of a waterfall or even make a short excursion in a damp meadow.

In the quiet-flowing stretches of the river or in the ponds they feed
and grow for years and years. They account for a good many young fishes.
Eventually, after five or six years in the case of the males, six to
eight years in the case of the females, the well-grown fishes, perhaps a
foot and a half to two feet long, are seized by a novel restlessness.
They are beginning to be mature. They put on a silvery jacket and become
large of eye, and they return to the sea. In getting away from the pond
it may be necessary to wriggle through the damp meadow-grass before
reaching the river. They travel by night and rather excitedly. The
Arctic Ocean is too cold for them and the North Sea too shallow. They
must go fa